part of the United Kingdom, lying in the northeastern quadrant of the island of Ireland, on the western continental periphery often characterized as Atlantic Europe. Northern Ireland is sometimes referred to as Ulster, although it includes only six of the nine counties which made up that historic Irish province. In proximity to Scotland and to sea channels leading to England and Wales, Northern Ireland has long witnessed generations of newcomers and emigrants, including Celts from continental Europe and Vikings, Normans, and Anglo-Saxons. In the 17th century, the period of the so-called Ulster plantation, thousands of Scottish Presbyterians were forcibly resettled and English military garrisons built, arrivals that would institutionalize the ethnic, religious, and political differences that eventually resulted in violent conflict. Since the 1920s, when Northern Ireland was officially separated from Ireland, it has been tormented by sectarian violence. Notwithstanding the peacemaking...